Automatic telecommunication exchange system



May 11, 1954 9 Shets-Sheeil Filed Jan. 13, 1951 I nvenlor MATNUS DEN HERTEI Attorn y May 11, 1954 M. DEN HERTOG AUTOMATIC TELECOMMUNICATTON EXCHANGE SYSTEM Filed Jan. 13, 1951 9 sheets-sheet 2 Inventor ,A Si, GTM NBG mb W Ql Wam A www mgm] SWWAH Gs M hun MART/NUS DEN HEPTOG l A w52 a w *llc v l vm ym 11|@ .mll 9 En A .Muzi c* l T@ Q QM hm, A uw $6 ...o h? .L A ma u uw T Sv lo my@ t| NQ. UQ .v Q s A Attorney May 1l, 1954 M. DEN HERTOG AUTOMATIC TELECOMMUNICATION EXCHANGE SYSTEM 9 Sheets-Sheet 5 Filed Jan. l5, 1951 MQ nk wwf K Inventor MART/NUS DEN HET By A Attorney May 11; T954 M. DEN HERToG 2,678,354

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AUTOMATIC TELECMMUNICATION EXCHANGE SYSTEM Filed Jan. 13, 1951 1 '9 Sheets-Sheet 9 Inventor MART/N05 DEN HERTOGI A itorney tion. 1

Patented May 11, 1954 AUTOMATIC TELECOMMUNICATION EXCHANGE SYSTEM Martinus den Hertog',l Antwerp, Belgium, assigner to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application January 13, 11951, seramo. 205,915

Claims priority, application Great Britain January 16, 1950 12 claims. (c1. 179-18) This invention relates to automatic telecommunication exchange systems.

One feature of the invention resides in arrangements whereby Selective operations for several calls' can proceed in a common control circuit for a number of selector switches, simultaneously with one another and with the actual setting of the associated selector switches.

Another feature of the invention resides in arrangements whereby register controllers themselves both control selection of an outlet` from a selector stage and record the identity of the selected outlet for subsequent use in controlling switching through at the selector stage to the selected outlet. f

A further feature relates to double test arrangements to prevent selection of the same outlet by selectors under control of diierent registe-rs, whether the selectors are part of the same or of different multi-switches. i Y

The scope of the invention is not limited to the above features and includes any other novel feature disclosed or foreshadowed in the following description of certain embodiments of the invention shown in the accompanying drawings in which:

Fig. 1 shows schematically the Way in which two registers control two individual selectors o f the same cross-bar multi-switch in lco-operation with the common control circuit of said multiswitch. f y

Fig. 2 shows suflicient of the circuit of a register controller to illustrate the invention.

Fig. 3 shows the circuits from a register controller through a link circuit to a rst group selector. y

Fig. 4 shows the individual circuits of anindividual group selector forming part of a crossbar multi-switch to illustrate the invention.

the similar equipment in the registenwhile f' Fig. 7 shows tables detailing the permutation code employed for transmitting the outlet'idenvtity from register to common controlcircuit Vin Fig. 6, While Fig. 8 shows a diagram of the Vtime-cycles employed to control selection. Fig. 9 shows a table indicating themethod of employing the impulses of Fig. 8 to controllselec- Fig. 1 illustrates the principle whereby each of a plurality of registers may simultaneously control a selection via different individual selectors forming part of the same multi-switch. A static outlet explorer in the common control circuit of the multi-switch is permanently available for signalling the availability of all outlets from the multi-switch to all registers connected to like multi-switches forselection purposes, regardless of whether the common control circuit is also in use for causing the through connection of one of its individual switches in accordance with a selection made by an associated register controller.

Assuming, for example, that two registers REA and REB represented in Fig. 1, each control a connection, register REA via selector SEA and register REB via selector SEB, forming part of the same multi-switch as selector SEA, the eX- ploring circuit at the electronic selection and bar operating circuit, (referred to hereinafter as the ESBO circuit), of this multi-switch will transmit for each free outlet an impulse in the corresponding time position from explorer No. 1 via break contacts har/1.2, hbm2 and the d Wires of both selectors to the corresponding register. Assuming now that one of the two registers receives an impulse corresponding to a free outlet of the wanted group, this impulse will coincide with the impulse supplied locally at the register to the comparator to indicate this wanted group, and this comparator will function and by means ofthe impulse regenerator pass on this impulse to vrecord the number of the outlet at the register. The register now closes the test circuit fortes'ting-on the ESBO circuit and renders this busy for switch operating purposes. The register lis now ablev to proceed with the transfer of the `outlet identity to the ESBO- via the c wire and break contact hdmi or hbmi at the selector concerned, after which it causes the operation of the horizontal magnet HAM or HBM at the -selector owing to which contacts ha'ml 5 or hbm 5 change over. Y

In this connection it will be seen that the a, c and d wires for this register are changed over to other circuits at the ESBO circuit, but the other register(s), which did not yet succeed in finding a free outlet in the Wanted group,` remains connected via the break contacts of magnet I-I at the respective selector(s) to wires V, III and VI at the ESBO. Since at the moment the first register succeeds in finding a free outlet of the Wanted group, the explorer No. 1 at the register is not prevented from transmitting further impulses, thiseXplorer is able to continue .mately`300 m. s.

to transmit its impulses to the second register and all further registers that may become engaged in conjunction with the same multi-selector, also during the time that the first register referred to has busied the ESBO circuit for switch operating purposes only and is in the actY of completing the connection by means of the ESBO circuit through the selector it is connected to.

During the time one selector is being switched through, all other calls using the same multiswitch are allowed to explore for free outlets and any register which during this interval finds a free outlet will record this on its own recording equipment and try to engage the ESBO circuit.

In the circuits to be described, the time during which a register may hold a record of a free outlet before it nds the ESBO circuit free is deter.- mined by the releasing time of a relay, approxi- If after `this interval the ESBO is not found free, the register cancels the records of the outlet found and starts to explore afresh. It isevident that the time during which a register may be caused to wait may be vvaried by suitable means, so that .even if two or three registers operating in conjunction with the same vESB() circuit would hold a record of a free outlet simultanevously,they would not cancel thisroutlet until they .had the time to complete their connection successively.

Figs. 2-.5 will now be described. The object of a group selector circuit is to effect the selection of a free outlet in a group chosen `from a plurality of groups under the control of a register `mon to allindividual switches and accessible to .said switches.

Vertical bars are also provided which cross all the horizontal bars rand control the selection of a particular outlet, which has to be connected to an individual switch, by the ac- -tion of the horizontal bar associated therewith.

The operation of the multi-switch will be described later in a more detailed manner.

A multi-selector comprises a number of individual selectors which share a common bare wire multiple and a common selecting mechanism. The bare wire multiple is arranged in a vertical Amanner and the individual selectors are arranged `in a horizontal manner in the multi-selector.

Each individual selector is provided with a set of inlet wires. If a multi-selector gives -access to -100 outlets,` for example, there will be 100 sets of vertical multiple wires, with any one of which sets any of the sets of inlet lwires may be brought into Contact. This contact is eifected by means of -flexible contact springs under the combined action of vertical and horizontal bars, `each horizontal bar corresponding to one of the individual selectors, or inlets, and each vertical bar corresponding to two of the outlets, or sets of Vertical wires. At each intersecting point of a horizontal inlet and two sets of vertical outlets the contacts may be established by the combined action of Ythe corresponding horizontal and vertical bars. .The actual contact is established `ley-means .of a contact pusher which moves all individual contacts of the set .of contacts concerned and'o which contact pushers one is provided for each of the intersecting points between horizontal and vertical bars. As at each intersectingpoint contact may loe-established between one inlet and either` of two outlets, one of these two outlets is selected by moving the contact pusher either in a forward or in a backward direction.

Summarising the above, there will be as many horizontal bars as there are individual selectors in a multi-switch. The number of vertical bars is equal to halfthenumber of outlets constituting the multiple of the multi-switch. At each intersecting point of horizontal and vertical bars a contact pusheris provided which, by forward or backward movement, may bring the inlet corresponding to the horizontal bar into contact with one of the two outlets corresponding to the vertical bar.

The vertical bars are arranged in pairs, so that for amulti-switch with outlets, the 50 vertical bars will be arranged in 25 pairs. In addition to these, a 26th pair is usuallyprovided for ,routine test purposes, but may be left out of consideration for the moment. For the control of each pair of vertical bars one common vertical magnet VM, Fig. 5, is provided, so that themultiswitch comprises .25 of these vertical magnets. Only one of the two vertical bars indicated by an operated vertical magnet maybecausedto move by the operation of one of .two common so-called vertical servo magnets-SVMA, SVMB, Fig, 5, which are provided in common for all 25 vertical magnets and which, in association with one of the vertical magnets which indicates the pair, causes one of the vertical bars of the pair to be moved upwards.

The selection of one ofthe 50 vertical bars therefore happens in two steps, first by the operation of one out of 25 vertical magnets indicating the-pair, and next by the operation of one out of two servo magnets-which operates one of the bars of the indicated pair.

The horizontal bar associated with each individual selector is associated with an individual control magnet HM, Fig. 4, which, when operated, indicates that the associated horizontal bar has 'to be moved. The actual movement takes place by means of one-out of two common so-cailed horizontal servo magnets SEMA, SI-IMB, Fig. 5, which causes the horizontal bar indicated by rthe operated horizontal magnet to be moved either inra-left-hand or in a right-hand direction. The movement of the horizontal bar therefore `happens-also in two steps, iirst by the operation of the individual horizontal magnet which indicates the horizontal barto be moved, and next by the oper-ation of one of the two horizontal servo magnets, which causes the horizontal bar indicated to be moved either to the right or to the left and which thereby causes the Contact pusher located at `.the intersection of the operated horizontal and vertical bars to be -moved either in a forward or a backward direction, thereby closing one set of contacts.

After these operations have happened, both the individual vertical magnet and the vertical servomagnet releases, so that the vertical bar again drops in its original posiiton. The common horizontal servomagnet operated also releases, but the individual horizontal magnet is held energised and thereby holds the horizontal bar mechanically locked in its ,operated position and therebykeeps acontact pusher moved out and the -contacts closed. When this horizontal magnet releases, the horizontal bar and the contact pusher are restored to their normal positionand the contacts are opened.

As regards the numbering of the outlets in relationto theoperation of the diierent selector magnets the following may be observed:

The 100 outlets are arranged in four rows of 25 each, whichare'numbered Uil-24, 25-49, 50-14 andTS-BS' respectively.lY HEachpair of vertical bars, and thereforey each ofthe vertical magnets VM, Fig. 5, corresponds to one outlet in each or" these four rows... Thus vertical magnet No. I corresponds to the rst outlet of each row (00, '25, 50 and), vertical magnet.No..2. to the second of. each row (0I, 26, 5l and 16) etc. All of. those vertical' bars which are lifted by the rst vertical servomagnet SVMA, Fig. 5, correspond to the firstV two rowsof 25.0ut'- lets. (UU-49), those lifted bythe second vertical servomagnet .SVMB, Fig. 5, correspondr to. the last .two rows,of`25 outlets (5U-99). It will be clear from this'that `by the successive operation ofvone vertical magnet VM and one vertical servo magnet SVMA or SVMB, two outlets will' be indicatedby thepperation of one vertical bar, viz. either one outlet each in rows I and 2 or one eachin rows 3 and 4.

After an individual horizontal magnet HM, Fig. 4, by its operation, has indicated the individual selector for which contact has to be established, the corresponding horizontal bar will be moved in one of twodirections, dependingon whether the horizontal servomagnet SHMA or SHMB, j Fig.' 5, operates. The contact pusher located .at the inter-section of the operated vertical and horizontal bars will accordingly be moved in'onefof Atwo directions and thereby establish contact with one of thetwo outlets indicated byrgtheloperated vertical bar. The arrangement ofthe horizontal servomagnets is such that SHMA causesgagcontact;to.be: closed either in rows l Olggand 'SHMB either in rows 2 or 4. Therefore `Sli-IMA controls outlets 00-24 and 50-14 and SHMB-.-Qutlets. 25-49 and v'I5-99.

A multi-switchof;thistype is employed in the ca sejofronehundred outlets: a ce1- tain number of individual `switches are provided, said number varyinggwith the traic requirements, eachnof thembeing adaptedto beV used independently to; establish a connection toa free outlet.

`Eeclrgof the switches has an individual selector-,circuit Fig. 4, comprisingV a horizontal electro-magnet` HM, forming part of the multi- Swltchtand a relay: GA.

Alcommon control circuit (Fig. 5) has been proyidedfor allthe` individual group selectors cfgav lmulti-switch. Thisl circuit, by employing electronicmmeans, as also a certain number of periodic cycles of Velectrical impulses, and under the, control of a register, Fig. 2, can carry out hunting and/or selecting operations for one of the .individual selectors, and control the operationof al vertical lbar and a horizontal bar of themulti-fswitch in order'to complete the connectionjemployed by the call, when the outlet has" been seized. The selection of a free outlet in, a'rparticularvgroup is made under the control of` theiflrst digit Aofthe desired subscribers number. finavailable iinalv selector, for instance, is chosen from ten different groups of selectors, e. g. each of said selectors serving 100 lines. This selection is made under the. control of the hundreds digit of the desired subscribers number,

trol the selection-a 6. tion may be made under the control of the register without direction relation to a particular digit, but as one of a Variable number of selections determined by a combination of digits-in accordance with a well-known method.

Thehundred outlets may be distributed in all conceivable ways, in any number of groups, usually ten. This number is in no Way limited.

The number of groups of outlets may be modified as desiredgthe number of outlets assigned to each group may bey modified as desired, according to the trail-lc requirements, and the outlets of each of the groups may be taken haphazard from `one of Vthe hundred outlets available.

The equipment and the circuit of the common control switch are always the same and are not dependent on the way in which the outlets are distributed in the various groups.

The register controlled comprises a device of any known type for'registering digits; the circuits employed for connecting the register con-- troller to the selector may also be carried out.

in accordance with well-known principles.

Consequently, it will be assumed that the digits` making up the number of the desired line have beenreceived anad registered, and that the reg-y ister controller, shown in Fig. 2, has been connected to the rst selection stage through the wires a, b, c, d. The earthapplied through" 0165 (Fig. 2) and the wire b cause the actuationoi' the relay GA, Fig. 4 in the first group selector through a back contact hb associated with the horizontal bar of the individual switch.

The relay GA, in operating, immediately causes the connection ofthe group selector circuit to the corresponding common controlY circuit, by respectively connecting the wires a, c and d to said common control circuit through the front contacts 90.5, ga3 and gall.

Moreover, the relayv GA prepares for itself a holding circuit through the wire e, inseries with the winding of the horizontal electromagnet HM and the front contact yal the said electromagnet cannot operate at the moment under consideration owing to the fact that earth is directly con-r nected rto two ends of its winding, the wire e being in fact directly earthed as shown in Fig. 32

The common control circuit is set in the operative position, earth being connected to saidv com-A mon control circuit through the following circuit: back contact hbl, associated with the horizontal bar, front contact ga2, lead I, back contacts svmaZ, svmb2 of the vertical servo magnets de-y scribed below, back contact gc3, relay GB, resistance and battery. The relay GB of the common controlA circuit operates, and through .its front contact gbl applies earth to the anodes of the'cold cathode tubes VRA', VRB, VRC;

A resistance Rg of 100,000 ohms has been pro-, vided in the common control circuit for each of the 100 outlets which can be reached through a group of selectors, this resistance being connected atl one of its ends tothe next selection stage through the wire e', Fig. 4. lf the outlet is free; the wire e is connected to negative battery po tential, through a back contact gal of the relay GA of the next selector, as is shown in the left of the circuit of the'rst selector, Fig. 4. When an outlet is busy, the potentialk on this.' lead will be'ground via front contacts ga of the preceding selector.

accessi .tial towards a pointof earth potential, associated with the grid of an amplifier tube ETI which forms one of the elements of a double triode ETI, ETZ, through three successive rectifier stages, placed in series ARCS, BRCS, CRCS, and rectifiers placed in shunt ARCP DROP. The rectiers placed in shunt, ARCP DRCP are connected to sources of current which will .be described in the following paragraphs.

Fig. 8 shows the cycles of impulses produced `by the different sources, said impulses being employed as time bases in order to obtain a 1000- element code.

Two principal groups of `impulses have been provided; the first are designated by the refer.- -ences Pa, Pb .and are produced by the sources PaS, rPbS shown in Fig. 2, and the others by Ra, Rb and are produced by the sources RaS, RbS The principal diierence between these two groups of impulses consists in their difference of potential. There are both positive-going and negative-going P pulses used, although Fig. 8 only shows the positivegoing pulses. The impulses P are always provided for insertion in the grid circuit of an ,amplifier tube, and their potentials have been determined accordingly. The impulses R are always provided for application to the control electrodes of cold cathode tubes and their potentials have been adapted to the operative conditions of said tubes.

Each of the groups Pa. and Ra. are produced by ve sources, PaSI5, RaSI-E, supplying an impulse for ve time units which succeed each other in accordance with a periodic cycle, the length of each of these impulses corresponds to the duration of the time unit on which the whole system is based and will be referred to in the following description as a unit of time.

Each of the two groups Pb, Rb are produced by five sources PbSI-, RbSI-5, supplying an impulse for ve time units which succeed each other in accordance with a periodic cycle. The length of each of the impulses corresponds to six time units and their period to thirty time units.

Each of the two group-s Pc and Rc are produced by four sources, PCS I-Il, RcSI-, of time impulses, the length and period of which respectively correspond to 30 and 120 time units.

The group Pd is produced by ten sources Pill-4b, of which the impulses correspond to 10S time units and the period to 1060 time units. These ten sources, like those of the other groups, produce time impulses displaced with respect to each other in such a way that the impulse produced by each of the sources comes after that of the preceding source.

The sources of the three first types of impulses, that is, Pa, Pb and Pc are employed to control the transmission of a signal constituted by a time impulse, as also the detection of a signal con.- stituted in the same manner. The simultaneous use of any three sources of different types makes it possible to obtain 5 5 4z100 time units. At the transmitting end these 100 time uni-ts are employed for scanning 100 outlets.

The sources for producing impulses PdI .Iii are employed for associating a special group indication to each of the outlets; thus in the case of outlets of a group selector, these sources are employed to characterise the group of said outlets.

Fig. 9 is a table showing combinations of send ing impulses Pa Pc which may be applied to three vgates supplying impulses to the register controllers; Fig. 5 shows a gate composed of rectiers which make it possible for outlets to send an impulse 4to the grid circuit of the amplifier tube ETI in 100l different time units, `the said tube retransmitting these impulses to the register. Fig. 9 shows combinations of impulses Pa Pc which may be applied to ythree successive stages of gates, such as ARCP, BRCP, CRCP, shown on the common control circuit of the selector (Fig. 5). The table .shows the impulses which must be used for the gates associated with each outlet. This table also shows in which time unit an impulse must be sent for each of the outlets.

The impulses applied to the gates ARCP, BRCP, and CRCP are in the negative direction. This means that the potential of the source is normally `at earth potential and becomes more negative at the time of the impulse. When any one of the sources is at earth potential, current flows through the associated rectier and through resistor Rg to the .source of negative potential on the wire e', and earth potential continues to appear .on the grid of tube ETI because of the potential drop across resistor Rg. It is only when .all three of the impulses Pa, Pb, and Pc are negative, that the associated rectiers are blocked and current then iiows from earth, through the resistor connected to the grid of tube ETI, through the rectifiers CROS, BROS, and ARCS, and through the resistor Rg .to .the e wire. This lowers the potential on the grid of tube ETI because of the potential drop in the resistor connected thereto.

The branch rectiers thus act as gates which can open or close the circuit to ETI: only when the gates are closed by the application of a relatively-negative potential by the associated sources can negative test potential be applied to ETI. It is thus only at this moment that the potential of the grid of tube ETI 4will be negative, provided that the outlet is free, that is to say, provides a negative potential.

It will now be seen that the three sets of impulses Pa, Pb and Po are applied to the gates in such a way that said gates pass the current at different time units for each of the 100 outlets; when a, circuit is free it sends negative impulses to the grid circuit of the tube ETI for a time unit which characterises this outlet. The manner of connecting the various gates, which makes it possible to obtain this result lfor the various outlets, numbers e0 `to is shown on the table in Fig. 9, which also shows the time units corresponding to the impulses transmitted by each of the outlets. Each outlet of a group selector is connected in the common control circuit (Fig. 5) with an individual gate which itself is connected to one of the sources of impulses PaI 5. Each ofthe twenty successive groups of five outlets, corresponding to the time units I. 5, 5 I0, and connected to the vvarious sources PaS, is associated with a second stage of gates constituted by the rectiers BRCS, BRCP. Four successive super-groups of five groups each are associated with a third stage of gates constituted by the rectiers CROS, CROP. Thus in all, there are l=20 gates in the second stage which are divided in turn into four groups of ve. The gates of 'each of these groups are respectively connected to the V9 ve sources o1' impulses PbI 5. The third stage of gates CRCS and CRCP common to said groups are each connected to one of the sources of impulses Pcl 4.

Each of the outlets connected to a gate associated with one of the sources of impulses Pal is also connected to a second gate DRCP, Which may be connected to one of the ten sources PdSl-ID supplying impulses Pdl to Pdl by connections which can be displaced as desired.

This connection characterises the group to which the outlet belongs, a connection terminating in a source PdSI or PdSZ indicating that the outlet belongs to group No. 1 or to group No. 2.

It is obvious that the potential supplied by Wire e will be absorbed in the resistance Rg at any moment, except When the source PdS connected to the particular gate supplies a relatively negative potential. In other words, for the outlets of group No. l, the grid of the ampliiier tube is only influenced during the time unitfwhen the source PdSI is sending out an impulse PdI, that is to say, during the time units I-I 00. Similarly the outlets forming part of the second group can only infiuence the grid potential in the time units IBI 200, and so on.

The result of this is that for each outlet an impulse from the wire e' can only be sent to the grid circuit in one of the 1000 time units, which characterises both the number of the outlet and the group to which said circuit belongs.

For example, the outlet No. 25, according to the table in Fig. 9, would send an impulse in time unit No. under the control of sources Pa., Pb and Pc. When this outlet is connected for example, to group No. 5, source Pdt at any moment will absorb the impulses transmitted by said circuit, except in the period corresponding to the fifth group of 100 time units, so that in these conditions an impulse is only sent in the 25th time unit of the fth period, that is to say, in time unit No. 425.

Recapitulating, when an outlet is free, negative battery potential will be present on its test lead e', and when the outlet is occupied, the potential on this lead will vbe a ground potential. The sources connected to the explorer constituted by the rectifier gate network are such that in the normal condition they provide a relatively positive potential and in the peak'condition, they provide a relatively negative potential. The result of this is that when an outlet is free, a negative impulse Will be supplied in the corresponding time unit to the grid of the triode ETI forming part of a double triode. This triode is connected as a cathode follower and consequently negative impulses will be supplied in the time units corresponding to all free outlets, from the cathode circuit of this triode via Wire V to the individual group selecto-rs from Where these impulses will be extended via contacts km2 back, yad front, HB3 back., to Wire d of the group selector which is extended in its turn to Wire d of the register circuit. A negative impulse received on wire d at the register will be converted into a positive impulse by the tube AT and these positive impulses are applied through a rectifier to the grid circuit of the tube RTI at the register. Thistube operates as a comparator, the comparison being effected means of a gate rectifier CTRC` associated with a tube CT of which the grid, via break `contact 112| is connected to one of the sources of 'impulses PcZI I0, as determined by the registering means of any well-known type on which a numericalY figure has been recorded and which l0v has not been represented on the drawing. The impulses thus applied are in the positive direction.

When impulses arrive from the common control circuit of which the time does not coincide with the impulses supplied from the source Pd connected, these impulses will not be able to operate the comparato-r tube RTI. This will be the case when these impulses are sent under the control of an outlet which does not belong to the wanted group. When an impulse arrives from a free outlet of the Wanted group, it will coincide with an impulse from the sources of impulses Pd connected at the register, and under these cireumstances the tube RTI will function and supply an impulse to the anode circuit of the pulse regenerator tube RTE. This tube, in conjunction 'with a transformer TP, TS will now supply a regenerated impulse the commencement of which is determined by the commencement of a very short impulse DI from a source DIS (Fig 2) which is applied tothe grid circuit of tube RTI, in a cycle having a pulse in every Pa pulse time position, but at times slightly staggered behind the starting times of the Pa pulses.

When pulses via tubes AT and CT coincide with a kpulse DI, tube RTI operates and causes current to flow in the primary windingvTP. of the transformer TP, TS. The tube RTZ together with the transformer TP, TS connecting the grid and anode circuits anda varistor or thermistor VS in parallel on the grid and cathode polarisation circuits form an impulse generator. Current fiow in the transformer primary TP causes iioW of current in the secondary TS of the transformer, and renders the potential of the grid of the regenerator tubes RTZ more positive. If the amplitude of the potential .applied is sufficient to bring the potential of the grid to a suitable value, taking the bias into account, the generator is started. The anode current begins to iiow through the winding TP of the transformer, the grid then becoming more positive, thus causing a fresh increase of the anode current. The potential of the grid is very rapidly brought to a value higher than that of the cathode; a stronger gridl current begins to flow, thus limiting any subsequent increase of the grid potential. At this moment, anode and grid currents begin to decrease, the latter decreasing more rapidly than the former, so that the diiierence between the ampere turns of the anode and grid windings increases rapidly.

After a certain time, which depends to a great extent on the self-inductance of the windings of the transformer and of the anode resistance of the tubes, the grid current is cancelled. From now on any reduction in the anode current causes, by induction, the appearance of a negative potential in the grid winding, which in turn causes another reduction of the anode current. The tube is thus rapidly de-energised and remains idle until the arrival of a fresh trigger impulse.

In this Way, the appearance of an impulse of nearly rectangular form is produced, the amplitude and duration of which depend neither on the amplitude nor the form of the trigger impulse.

The loading resistance RRS, placed in the cathode circuit of the generator, makes it possible to transform the current impulse into a voltage impulse, said voltage being maintained at substantially the same value for the whole duration of the impulse.

One impulse Will be generated for each trigger impulse applied. to the anode, after which the tube returns to normal. The voltage impulse produced on the terminals of the cathode load resistance of RT2 is applied to the control elecn trodes of groups of cold cathode tubes Vli 5, Vbl- 5, Vcl .4, Vd.

The Va, Vb, Vc tubes are each controlled by a rectiier'connected between the control electrode thereof and one of the time-pulse sources Ras, RbS, RCS, producing impulses Ra, Rb, Rc, acting in the positive direction, of which the impulse cycleshave been shown in Fig. 8, said tubes being ionizable at specific times only. Thus, the tube Valis controlledv by the impulses Rai, the tube V412 by the impulses RaZ and so on, so that a tube suchas Val can only be ionised in one of the time units in which the source RaSI is transmitting an impulse Rai i. e. according to Fig. 8, in time units I, 6, Il etc.

Similarly, the tubes Vblf 5 are each connected` to one ofthe sources RbSl 5, producing impulses Rbl 5, through. a rectifier, so that a. tube suchas Vbl, for example, can only be ionised during one ofthe groupsof time units in which the source RbSI is transmitting an impulse Rbl, viz in time units i 5', 26 35, y5I 55, etc,

The tubes Vcl 4 are also controlled by impulses Rel 4, of which the respective transmission time units may be found in Fig. 8.

Finally, there is a further last tube Vd which is not controlled by rectiers, and thus can be ionised when it receives an impulse arriving in any time unit.

It is clear from the above that an impulse arriving in any time unit will always ionise one tube to each of the three groups Va, Vb, V c, plus tube Vd. A combination of tubes, one from each group, is characteristic of each of the time units, and they holdin their anode-cathode circuits Via the corresponding relays in the groups Aa Ae, Ba Be, Ca Cd to make contact bl of normally energised relay B: battery B, dtl back, 11H3 back earth.

Tube Vd acts by. means of a rectifier DRC and a potentiometer DPT on the potential at the grid of a suppressor tube ST, which controls the cathode potentialY of tube RTI. As soon as tube Vd has ionised, the potential at the potentiometer is so changed that the grid potential of ST and thereby its cathode potential and that of tube RTI are changed to a value at which RTI is disabled from responding to further impulses. The cold cathode tubes will therefore be able to receive only a single impulse, indicating the rst ofthe free outlets of the wanted group found by the explorer.

In series with tube V d, relay F has operated.l and this atcontact f2 short-circuits the winding of relay B. Relay B is is assumedto be operated from the moment the register was engaged and had prepared at its contact bl, a ground to the anode circuits of all cathode tubes. The short circuit by contact f2 does not `take effect immediately, because B is made very slow to release under these conditions. At make contact ,f3 no action takes place. Make contact fl, however, closes a circuit for the test relay T to wire a, which, via the selector, is extended to wire VI of the common control circuit, to which wire battery potential is connected via 255W and break contacts gc and gf2. 1f the common control circuit is free, i. e. if it is not engaged by another register for effecting a connection on a multiselector, relay T at. the register concerned will be-able to energise to this test potential and by closing at; contact tl its low resistance winding in series with a winding of relay Dt, renders this test potential busy. Relay Dt now also operates andatbreak contact dtl now fully opens the circuit. of B, so that this releases quickly. As a consequence, ground is removed at bl from the anoder circuit of all cold cathode tubes, so that those tubes ionised and their relays are now able to hold in series with relay U via break okl, and make contactv dtlv to ground. As a consequence, relay U operates and in its turn at contact ul energises relay V to the same ground. Relay V prepares a locking ground for itself and U via contacts u3 and cl3, independent of contact dtG.

In the condition of the registerl circuit now described this is ready to transmit the indication of the identity of the outlet selected to the common control circuit. In the circuit in question this happensgby using the same impulsing code as used for the exploration of the outlets, i. e. each outlet -is'represented by one time position: in recurring cycles of 100 time positions. In order, therefore, to signal the outlets to be connected an impulse is to be transferred in a: time position corresponding to the selected outlet number. This happens-by means of a tube BT of which the grid circuit is controlled by three sets of gates, each gate comprising a rectifier and a contact of one of the recording relays andbeing connected to a corresponding pulse source. The'rst set of gates are connected via front contacts of the recording relayszAa, to Ae tov one of the sources Pa! 5, the second set via front contacts of the recording relays Ba to Be to one of the sources Pbl 5-and the third set via contact of the recording relays Ca to Cd to onevoi the sources Pcl- 4. The arrangement isv such that only in one time position in which the pulses from all of the three sources connected coincide, the grid of tube BT will be rendered relatively positive, so that then its cathodev will supply a positive-impulse via back contact ckllvto wire c. Thus it will be seen that here the'positive-going P pulses are-used. This impulse is transmitted via wire c of the selector and contacts hb2 back, ac3 front, hm! back, Fig. 4, to wire III'of the common control circuit, which is connected again to three sets of cold cathode tubes VRA, VRB, VRC, arranged in a similarY manner as those at the register circuit. Asa consequence, one'of each set of these tubes willionise in accordance with the outlet to be connected and cause one of each of the three sets; of anode relays to energise. The first two sets of these relays,- Ara to Are and Bra to Bre servetodetermine which of the 25 vertical magnets VM mustbe-energised One of these magnetsv is operated by a Contact closed via a make contact of one'of each of these two sets of relays in an obvious circuit as'indicated in Fig. 5. The set-of four relays Cra to Grd determines which of the-servo magnets must operate-inorder to effect connection with the wanted outlet. As may be seen on the drawing the vertical servo magnet SVMA willenergise when relay Cm or Crb has operated which correspondsV with one of the first two rows of 25 outlets and SVMB Will operate when either relay Cre or Crd, which each correm spond toene of thetwo last rows of 25 outlets, has operated. The operating circuit for SVMA. or SVMB is completed, as soon as one of the Verticalfmagnetsl VM.r has energized, via: a make contact Avmll of 'onezrotthese magnetsand wvia a makecontact ycl or ge' -on one .of two relays GD or GE. Relay GD is operated via make contact cm2 or c1'c2 for outlets!) to 24 and 50 to 14, whereas GE energises for outlets 25 to 49 and 15 to 99 via front contacts crb2 or crdZ.

Meanwhile relay GF` in the common control circuit has also operated by virtue of rbeing connected via rectiers in parallel with the cathode resistance of each of the three groups of cold cathode tubes. At make contact gfl this relay short-circuits the winding of relay GB which previously had operated from ground provided via break contact. hbi and make contact ga2 at the selector circuit, and which by its operation had provided on contact gbl a ground to the anode circuits of all cold cathode tubes VRA, VRB, VRC. The short-circuit of this relay by contact gbl does not immediately takeeffect, because GB is very slow'.v to release under these conditions. 1 1- vBreak contact gf2 opensthe test potential to wire VI and by this causes the release of the test relays T and Dt at the register circuit, thereby signalling to this circuit that the wanted outlet has been recorded in the common control circuit. Release of relay Dt Fig. 2 closes a circuit via break contact dt3 and make contact 'Ulli -for the operation of relay Ok at the register, which locks itself to its own make contact ok! underthe control of contact Vi 6. Contacts ok'l open the holding circuit in which the outlet identity recording relays Aa, to Ae, Ba to Be and Ca to Cd together with relay U were held energised. These recording relays therefore release in readiness forl receiving a nextrrecording for the following selection. The release of .U at contact u3 opens theholding ground via M9, '020, for` relay V,but

the cord circuit, Fig. 3. Both GA and I-IMhold in this circuit, HM changing over ,its contactsv hml, hmZ, hm3. The test relay T is now con.-`

nected Via u2 back, Fig. 2, JLwl'! front, Vwire a, Figs.`

3 and 4, hbd back, co5 front, hm3 front, wire, VII, relay GC and one of contacts 907.3 or gek to one of the vertical bar contacts VBAI, VBAL, VBBI or VBB2. Each of the vertical bars, as explained above, is associated with-two outlets.. viz. one of the bars of a pair is associated with one of the outlets of rows 0B to-24 and 25 to 49, i..

the other bar of each pair being associated with one of the outlets of -rowsf50 to 'I4 and l5 to 99. Depending on which ofthe relays Cra to Cro! has energized, a circuit will now be established to only a single contact corresponding tov one of the outlets. Assuming e. g. that one of the outlets in group 00 to 24 had been selected, relay Cra' would have operated and caused the energisation of servo magnet SVMA which controls all vertical bars corresponding to outlets 00 to 49. At the same time Crar would have caused the operation of GD, so that of the two groups of 25 contacts associated with each of VBAI and VBAZ, of which one is closed by the combined action of VM and SVMA, only that of the rst group, yiz. Si! to 24,. could be connected via contact4 'gd3. Depending on which of the 25 vertical bars is energised, one of the outlets of this group of 25 will therefore be connected and the test circuit. just referred to will be extended via the contact vcon-- of other registers may operate on this potential.

any more, but at the same time by the removal of the negative potential from the test lead, the explorer at the common control circuit will no longer be able to produce for this outlet a negative impulse.

Assuming that this test succeeds, relays T and Dt operate a second time at the register and asl already described above, Dt recloses its contact dts and reestablishes ground to relay V early enough to cause this to hold via its make contact 1120. Relay U, however, remains de-energised.

Ground from make contact oke is now extended via the c conductor, which at the selector circuitV is extended via hb2 back, ya 3 front, hm! front, to wire II of the common control circuit, where it causes the operation via make contact cd2 or Ice2 of one of the horizontal servo magnets SI-IMA or S'HMB, according to whether relay GD or GE was energised. The horizontal servo magnet operated immedaitely closes a holding circuit for itself to its makecontact shmal or shmbl,

independent from its energising circuit from the register.

The operation of the horizontal servo magnet at the common controlcircuit causes the displacement ot the horizontal bar of the individual selector for which magnet HM has already energised, and due to this the break contacts hbl 4 controlled by the horizontal bar are opened, owing to whichthe individual selector circuit is now disconnected from the common control circuit.

The `test potential which was provided from the test lead of the outlet selected is interrupted at break contact hb, this test potential now being busied by the fact that ground is connected from the individual selector circuit to the test lead of the outlet via contact E= and make contact ga. The disconnection of free test potential from lead a causes the release of the Vtest relays T and Dt at thegregister. The opening vof contacts dt .releases relay V,and with contacts ell, fl, and

dtd open, relays D and Dt are disconnected from wire a. YThe release of relay V also releases relay OK and ground is reconnected at olc5 back to lead b, so that now via this wire the relay A in the next selector may be caused to operate.

It will be seen that the register is nowV again in the original'condition, which was assumed to exist at 'the' moment the selection described com# menced.

A"In caseit occurs that two or more registers, operating in yconjunction with one common control circuit haveV tested on the same outlet simultaneously, these yregisters all try to operate their testrelays T and Dt immediately after the number of this outlet has been recorded at the register. As the test potential is given at the common control circuit via a resistance of 25010, only one of the Vpairs of relays at the registers concerned will b'e able to operate de-nitely on this test po` cessful registers, of which the ltest relay Dt doesl not operate will relapse to the condition in which free outlets of the wanted group are emplored in the following manner.

averages-r.

It has been seen that at the moment, the:

identity of the outlet is recorded at the register by the operation of a combination of cold cathode tubes and their anode relays, relay F also energizes which at f2 short-circuits relay B. Even if the test relay Dt does not succeed 1n operating, relay B will finally be caused to release after some delay by being short-circuited at f2 and accordingly the cold cathode tubes are deenergised and their anode relays released, there being no holding circuit via the winding of relay U, because relay Dt had failed to operate and maintains the holding circuit open at make contact dt. The record of the outlet tested has therefore been completely removed and after a while relay F releases, owing to the extinctionv of tube Vd, and B re-energises and re-establishes the. selecting condition.

The case may. occur that registers are connectedto different common control circuits of which the multi-selectors have access to the same group of outlets or of which at least some of the outlets are provided in common for the two multi-switches concerned. In this case, when one outlet connected to two different multiswitches is seized simultaneously by two registers engaged with different common control circuits, these registers will each test, after having recorded the outlet identified, on a separate common control circuit and, therefore, will proceed with. the operation of transferring the identity of the outlet selected each to their respective common control circuit in the manner described above. When at each of the two common control circuits concerned, the vertical bars are operated in consequencer thereof, the first thing to happen is that the registers make a test on the test lead of the outlet. When this happens with two registers simultaneously, only. one register will be able to energise its test relays on the test potential providedfrom the outlet and this will be able to proceed with the connectionv as described. The unsuccessful register of which the testrelays did not succeed in operating when the outlet was tested, will now relapse again in the selecting condition in the following manner:

It will be seen that the test on the outlet commences after the release of relay U, which connects the test relays to wire a via break contact u2 and make contact vII. Relay U at the same time at make contact u3 opens one holding circuit for relay V. Asdescribed above, this relay normally is slow enough in releasing to remain operated until the test relays have re-energised, so that thereby Dt is able to reclose the other holding circuitof V at make contact dt. In case, however, the test does not succeed, contacts dt@ do not close and accordingly relay V will release. Relay V immediately opens the circuit for the test relays at make Contact 1211 and also opens the holding circuit for relay OK at make contact UIB. -Relay OK by releasing now recloses ground to wire b at olc back, owing to which the horizontal magnet HM at the selector is again short-circuited via break contact HB5, so that the horizontal magnet releases and restores the selector to the condition in which it permits of hunting for a free outlet. At the same time, reclosure of break contact vI8 at the register circuit connects earth via UIB, dtI back, to energise relay B and prepare the register for recording the identity of a free outlet found. All circuits are therefore again in the selecting condition.

Inl the circuitsv asdescribed so far, the transfer' of the identity of the outlet. selectedfrom the register to the ESBO circuit happens by means of a time-pulse cycle-in which eachv time position identifies a different outlet;

As the transmission of outlet identification pulses from'the common control circuit can continue without a break, the information to be conveyed from the register to the ESBO is limited to the identity of the outlet and there is no impulse suppressor in the common control circuit. This permits of a cheaper signalling method. As there is only a single` wire available between the register and the ESBO for this purpose, a method has to be chosen, however, which permits of transferring this signal by a singlewire in a rapid manner. One possible way of doing this has lbeen illustrated in Fig. 6, which at its left-hand side shows a part of the registerl circuit and at its right-hand siole a part of. the common control circuit.

The part of the register circuit indicated refers particularly to the apparatus required for the transmission of the selected outlets identity from the register to the control circuit. This apparatus is similar to that employed in Fig. 2, viz. it comprises a tube BT of which the cathode circuit is connected to the c: wire and of which the grid circuit is connected to a number of impulse sources under the control. of the outlet identity recording relays at the register. For the purpose of transfer now to be described, use 1s made of permutation code for which impulses P aI 6 are employed in different combinations. It will be assumed that six impulses Pa are provided instead of five, and therefore six.

tubes Val 6 and= sixrelays Aal 6.

Each Pb pulse now equals six Pa pulses instead of five, as in Fig. 8. The code employed has been shown in tables on Fig. '7. It will be seen that I, 2 or 3 lmpulses Pal 5 produced'by one or a combination ofthe sources Pasl 6 may be sent consecutively via the c wire, and will cause thereby the operation of a corresponding number of cold cathode tubes VRAIA 6, VRBI, 2, at the common control circuit as well as their anode relays Ara/Arf, Bra, Brb.

In Fig. 6, these anode relayshave been represented together with their contacts whichv are required to obtain the operation of the different selector magnets in the same manner as is indica-ted in Fig. 5. It will be seen that the control circuit now only comprises a total of 8 cold cathode tubes and 8'V anode relays instead of l5 as in Fig. 5.

The transfer of'a permutation code from the register to the selector control circuit happens as follows.

When the outlet identity recording relays Aa...Af,B.a...Be,Ca...Cdattheregyister have operated, the cathode of tube BT is connected to the c wire, whiclrvia the selector individual circuit, not shown in Fig. 6, extends to the control electrodes of allY cold cathode tubes VRAI 6,-VRBI, 2, in the common control circuit, Fig. 6.

A potential of v. is connected via aresistance to the grid of tube BT, sol that this, by virtue of being connected as a cathode follower, normally holds its cathode also ata potential near to 150 v.

The grid circuit is connected via two separatingfrectifi'ers LRC, RRC, to two gate circuits; each of which may independently provide a positive impulse to the grid.

The connection via the left-hand rectier LRC is controlled in the iirst place by a group pulse gate GPG! which is connected to the source Pb! of impulses and which maintains this connection at 150 v., except during the time source Pb! provides a relatively positive impulse, The connection is further extended via a resistance R! to a number of further separating rectiiers which, via contacts of the outlet identity recording relays Azz/Af, Bca/Be, Ca/Cd, in different combinations may be respectively connected to one of the sources of impulses Pia! to PaS. The arrangement is such that only when a positive impulse from one of the sources of impulses Pa! to PCL6 coincides with a positive impulse Pb! the grid lead may assume a relatively positive potential.

It may be seen namely that so long as Pb! is relatively negative, a positive impulse from any of the sources of impulses Pa! to Pa will not affect the grid circuit, because the gate in series with Pb! is conductive and maintains a negative potential on the grid, the difference of potential prevailing between the grid lead and a positive potential from any of sources of impulses Pa! to Pa being absorbed in Rl.

When Pb! is relatively positive alone, without any of sources of impulses Pa! to Pa, the gate in series with Pb! is non-conductive and the grid is maintained negative by its grid resistance.

Therefore, depending on the combination of recording relays operated one or more impulses will be supplied in turn from one or more of the sources of impulses Pal to Pat during the period during which source Pb! of impulse is relatively positive.

These impulses are transmitted by BT via the c wire and cause the ionisation of a corresponding number of the cold cathode tubes of the set VRAI 6 in the common control circuit. These tubes are individually controlled by impulses Ra! 6 respectively, and are also controlled as a group by a gate connected to the source of impulses Rbl, which at this time is relatively positive and renders the gate non-conductive, so that the pulses are not absorbed thereby.

Pulse potential during period Rb! is not able to ionise either of the set of tubes VRBI, 2, because these are controlled by a gate connected to the source of impulses Rb2, which during the period Rb! is negative, so that it maintains the control electrodes of tube Vbl, 2 negative.

The grid circuit of tube BT is further controlled via the right-hand rectifier RRC by a second gate, connected to the source PbZ of impulses of which the impulse periods do not coincide with those of Pbl. Further this circuit is extended via resistance R2 and further contacts of the outlet identity recording relays to sources of impulses Pal and Paz. In a similar Way to that described above, positive impulses may be supplied via this circuit to the grid of BT when a positive impulse Pa! or Paz coincides with a positive impulse Pb2.

Depending on the contacts on the recording relays closed, one, or both or none of the impulses Pal and Paz may be applied during the period in which P122 is relatively positive,v when impulses do appear on the grid of BT, they are also transmitted to the common control circuit lwhere they are able to ionise the tubes VRBI, 2, in a corresponding combination, without being 18 able to aiect the tubes VRA! 6*, owing to the functions of the gates connected to sources of yimpulses R62 and Rb! respectively, which control these two sets of tubes.

The network of contacts of the recording relays shown fanning out from arf! are arranged so that each combination of pulses in period Rb! will cause the operation of a corresponding one of the twenty-six individual vertical magnets.

As an alternative to the arrangement shown in Fig. 6, it may be considered to convert the permutation code received on tubesVa! 6 into an indication for operating one of the 26 vertical bars, not in an electrical manner but in a mechanical manner. This is, the selector in this case should not comprise 26 Vertical magnets each controlling a pair of vertical bars as previously described, but there would be for example, six code bar magnets which act on an equal number of code bars that may be displaced in different combinations and thereby provide in a mechanical manner one of the 26 desired combinations for action on the vertical bars. In such a case it might be advantageous not to use a permutatien code of six signals as illustrated in Figs. 6 and 7, but of live signals so as to reduce the number of code bars from `6 to 5, this being suicient to select 26 different combinations.

In the embodiment described, the invention was applied to a system in which a register-controller has access to the selection stages both forward and backward solely via the cord-circuits and the conversational circuits to the respective common control or ESBO circuits in turn.

An alternative system is described in my copending application Serial No. 206,691, led January 13, 1951, in which a register controller has direct and yindividual access via so-called ESBO connectors to the common control or ESBO circuits at the respective selection stages without passing over any part of the conversational connections.

The ESBO connectors provide suiiicient parallel connecting leads between the register controller and an ESBO to allow of direct operation of the selector switch under control of the outletidentity registering cold cathode tubes and relays in the register. This obviates the need for outletidentity registering equipment in the ESBOS, and the need for outlet-identity signalling between register-controller and ESBO as in the embodiment described above.

While the principles of the invention have been described above in connection with specific embodiments, and particular modiiications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention.

What I claim is:

1. An automatic telecommunication exchange comprising a pluraltiy of outlets, means for giving each free outlet an electrical characteristic, a plurality of individual selectors each having access to a group of said outlets, a register controller connected to said individual selectors, a common control circuit for said selectors connected to said selectors, gating means in said control circuit connected to said outlets and responsive to the electrical characteristic indicating the free condition of an outlet for producing a voltage impulse whose position in time is characteristic of said outlet, means for transmitting all such voltage impulses to saidN register controller, meansin said register controller including a plurality of registering devices and a gating 19 network connected thereto responsive to said time-positioned voltage impulses for registering in said devices the identity of the outlet charu acterized by the first of said received impulses, means controlled by said registering means for transmitting a signal characteristic or" said outlet to said common control circuit, and means in said common control circuit responsive to said signal for connecting said selector to said outlet.

2. An automatic telecommunication exchange, as claimed in claim 1, in which the means in the common control circuit for connecting the selector to the outlet comprises means for registering the identity of said outlet in response to the received signal, and means for setting the selector under control oi said last-mentioned registering means.

3. An automatic telecommunication exchange, as claimed in claim 2, further comprising means in the register controller under control oi" the means for setting the selector for making a second test to determine the free condition of the outlet selected, and means in the register controller under control of said second test means for releasing said selector if said second test is not successful.

4. An automatic telecommunication exchange, as claimed in claim i, further comprising means under control of the means for connecting the selector to the selected outlet for releasing the register controller when the selector had been connected to the outlet.

5. An automatic telecommunication exchange, as claimed in claim Ai, further comprising means under control of the means for connecting' the selector to the selected outlet for disconnecting the common control circuit from said selector.

6. An automatic telecommunication exchange, as claimed in claim 1, in which the means in the control circuit responsive to the free condition of an outlet for producing a voltage impulse whose position in time is characteristic of said outlet compri a plurality of voltage impulse sources, each source producing' a train of impulses having a position in time different :from that of the impulses produced by every other source, a. common return connection for said sources, a resistor having one end connected to said common return connection, a plurality of branch circuits eachY connected between the other end oi said resistor and one of the outlets, a source of voltage at each outlet, means for connecting said source between said outlet and said common return connection when said outlet is free, whereby a current will normally flow through said resistor and a branch circuit oonnected to a free outlet, a rst rectifier connected in each branch circuit adjacent said resistor and poled so as to permit said current to now, a second rectifier connected to each branch circuit, means for connecting a diierent pulse-train source to each second rectiiier, the polarity of said voltage source, said voltage impulse trains, and said second rectiers, being such that current is prevented from iiowing through a branch circuit leading to a free outlet whenever a voltage impulse is applied to the second rectiiier connected to said branch circuit, whereby the Voltage of the junction of said resistor and said branch circuit is changed at the time of the impulse applied to said second rectifier, and means for transmitting the change in voltage so produced to the register controller.

7. An automatic telecommunication exchange, as claimed in claim 6, in which the outlets are divided into groups and further comprising' a second group of repetitive voltage impulse sources connected to the common return connection, the impulses of each source in said second group having a position in time diierent from those of every other source and a duration equal to the repetition period of the impulse of the iirst group of sources, a plurality of second branch circuits, each connected beta/'een the resistor and a group of the rst-mentioned branch circuits, a rectifier included in each of said second branch circuits, poled so as to permit current to iiow through said resistor to the source of voltage at a free outlet, a rectifier connected to each second branch circuit, and means for connecting one of said second group of impulse sources to each of said last-mentioned rectifiers, said sources and said last-mentioned rectifiers being so poled that when an impulse is applied to a rectiiier the current will be blocked from flowing through said resistor, the means in said register controller ,For responding to the voltage impulse transmitted from said common control circuit comprising coincident circuit having two inputs, means for selectively applying the voltage impulses from one of said second group of sources to one of said input circuits, and means or applying the voltage impulses received from said common control circuit to the other of said input circuits, whereby an output of said coincidence circuit will only be produced when the impulses coincide and a free outlet in any group may thus be selected.

8. An automatic telecommunication exchange, as claimed in claim 7, in which the means in the common control circuit for connecting the selector to the outlet comprises means for registering the identity of said outlet in response to the received signal and means for setting the selector under control of said last-mentioned registering means.

9. An automatic telecommunication exchange,- as claimed in claim 8, further comprising meansV in the register controller under controlv of the means for setting the selector for making a second test to determine the free condition of the outlet selected, and means in said register contransmitting a Voltage impulse at the same time position as that received by said register con'- troller from said common control circuit, and inv which the means in said common control circuit. responsive to said signal comprises means for,

registering the identity of the iree outlet in ace cordance with the time positioned voltage im pulse so received.

1l. An automatic telecommunication exchange, as claimed inY claim 1, in which theY means for transmitting a signal from the register controller to the common control circuit comprises means controlled by the registering means for transmitting a Voltage impulse having an arbitrary time relation to the time oi the voltage impulse received from saidy common control circuit, and in which the means in said common. control circuit responsive to said signal comprises' means for registering the identity-of the free outf-vk let in accordance withthe time positioned voltage impulse so received. l

2l 22 12. An automatic telecommunication ex- References Cited in the file of this patent change, as claimed claim 1, in which there UNITED STATES PATENTS are a plurality of register controllers and a plurality of common control circuits; each common Number Name Date control circuit being available to each register 5 1,757,446 Wrlght May 6 1930 controller, further comprising means in each reg- 2454809 Kruithof NOV' 30 1948 ister controller for testing Whether a common control circuit is in use, and means in each common control circuit for rendering it busy to said test means when it is in use for controlling the 10 setting of a selector. 

